First read this :
Normal serum prolactin levels vary between 5 and 25 ng/ml in females although physiological and diurnal variations occur. Serum prolactin levels are higher in the afternoon than in the morning, and hence should preferably be measured in the morning. Hyperprolactinemia is usually defined as fasting levels of above 20 ng/ml in men and above 25 ng/ml in women at least 2 hours after waking up. Unless the prolactin levels are markedly elevated, the investigation should be repeated before labeling the patient as hyperprolactinemic. Even one normal value should be considered as normal and an isolated raised one should be discarded as spurious. Other common conditions which must be excluded when considering raised prolactin levels are non-fasting sample, excessive exercise, history of drug intake, chest wall surgery or trauma, renal disease, cirrhosis, and seizure within 1-2 hours. These conditions usually cause PRL elevation of <50 ng/ml.
Hyperprolactinemia without an identified cause requires imaging of the hypothalamic-pituitary area. A mildly elevated serum prolactin level may be due to a nonfunctioning pituitary adenoma or craniopharyngioma compressing the pituitary stalk, but high prolactin levels are commonly associated with a prolactin secreting prolactinoma. Although computerized axial tomography (CAT) scan can be used, magnetic resonance imaging (MRI) with gadolinium enhancement provides the best visualization of the sellar area. A prolactinoma is likely if the prolactin level is greater than 250 ng/mL and a level of 500 ng/mL or greater is diagnostic of a macroprolactinoma. Selected drugs including risperidone and metoclopramide may cause prolactin elevations above 200 ng/mL.
In cases where other causes of hyperprolactinemia have been excluded and no adenoma can be visualized with MRI, the hyperprolactinemia is referred to as “idiopathic”
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